Methods for packaging and sterilizing elastomeric articles, and packaged elastomeric articles produced thereby

ABSTRACT

The present invention relates generally to methods of sterilizing elastomeric articles in a manner that prevents and/or reduces degradation to the articles, particularly degradation that may be caused and/or accelerated by sterilization techniques such as gamma irradiation, x-ray irradiation, and electron-beam processing. The methods include packaging the elastomeric articles in order to improve their resistance to degradation. In certain aspects of the invention, packaged elastomeric articles, optionally containing one or more antidegradants, such as antioxidant and/or antiozonant compounds, are also provided. The methods of providing degradation-resistant elastomeric articles in accordance with the present invention may also be used to reduce the occurrence of cracking and discoloration in elastomeric articles, regardless of whether they are subjected to sterilization.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/297,593 filed on Jan. 22, 2010, titled “METHODS FOR PACKAGING ANDSTERILIZING ELASTOMERIC ARTICLES, AND PACKAGED ELASTOMERIC ARTICLESPRODUCED THEREBY” and U.S. Provisional Patent Application No. 61/331,204filed on May 4, 2010, titled “METHODS FOR PACKAGING AND STERILIZINGELASTOMERIC ARTICLES, AND PACKAGED ELASTOMERIC ARTICLES PRODUCEDTHEREBY”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods of packaging andsterilizing elastomeric articles in a manner that prevents and/orreduces degradation to the articles, particularly degradation that maybe caused and/or accelerated by sterilization techniques such as gammairradiation, x-ray irradiation, and electron-beam processing. In certainaspects of the invention, packaged elastomeric articles containing oneor more antidegradants, such as antioxidant and/or antiozonantcompounds, are also provided. The methods of providingdegradation-resistant elastomeric articles in accordance with thepresent invention may also be used to reduce the occurrence of crackingand discoloration in elastomeric articles, regardless of whether theyare subjected to sterilization.

2. Description of Related Art

Although the technology involved in the production of syntheticpolyisoprene (PI) latex has been used for a long period of time,synthetic PI latex has only been used commercially for glovemanufacturing for about the last decade. This was in part because theprice of synthetic PI latex is significantly higher than natural rubberlatex, although both latices have polyisoprene as their activeingredients.

However, in view of the increased level of awareness regarding allergiesto proteins present in natural rubber latex, there has been a shifttowards the use of synthetic latices that do not contain natural rubberlatex proteins, especially for use in making medical devices that comeinto contact with the skin. Taking cost and performance intoconsideration, synthetic latices that are suitable for glove manufactureinclude nitrile latex and polyurethane latex for examination gloves, andpolychloroprene latex and PI latex for surgical gloves. For surgicalgloves, PI latex is preferred over polychloroprene, even though it ismore expensive, because it provides the gloves with properties thatmimic those of natural rubber, particularly tensile strength, ultimateelongation, softness and comfortable feel.

While the synthetic PI polymer is chemically similar to the PI polymerin natural rubber, there are some differences in the chemical structureof the polymer. In addition, there are also differences between thecompositions of synthetic PI latex and natural rubber latex. Dependingon the catalyst used for preparing the PI, synthetic PI contains about90 to 98.5% cis-polyisoprene, 1 to 5% trans-polyisoprene and 0.5 to 5%other forms of polyisoprene. The PI in natural rubber comprises about98% cis-polyisoprene and 2% trans-polyisoprene. In terms of overallcomposition, natural rubber latex comprises about 94% PI latex particlesand about 6% non-rubber materials, whereas synthetic PI latex comprisesabout 97-99% PI latex particles and about 1-3% colloidal stabilizers.The colloidal stabilizers, such as surfactants or carboxylic acid soaps,help to keep the dispersed PI particles stable in the aqueous phase. Thenon-rubber materials in natural rubber comprise proteins, lipids, fattyacid soaps, etc. These non-rubber materials play an important role inthe vulcanization of rubber in the latex and some are believed to haveantioxidant properties.

Due to these differences between synthetic PI latex and natural rubberlatex, in terms of both the compositions of the PI polymers and theoverall compositions, the vulcanization formulation for crosslinking thePI polymers in the latices is different for each of the two types of PIlatex. Since commercial synthetic PI latex is relatively new as comparedto natural rubber latex, the amount of published information on thecompounding formulations for synthetic PI latex is limited. A briefreview is provided below.

Generally, the compounding formulation for vulcanization of rubbercomprises the following classes of materials (a) crosslinking agents(usually sulfur or sulfur donors), (b) vulcanization accelerators, (c)vulcanization activators, and (d) antidegradants. For reference, thefollowing abbreviations are used in this application: ZDEC—Zincdiethyldithiocarbamate, ZDBC—Zinc dibutyldithiocarbamate, ZDNC—Zincdiisononyldithiocarbamate, ZDBeC—Zinc dibenzyldithiocarbamate,TMTD—Tetramethyl thiuram disulfide, TETD—Tetraethyl thiuram disulfide,TBeTD—Tetrabenzyl thiuram disulfide, MBT—2-mercaptobenzothiozole,ZMBT—Zinc 2-mercaptobenzothiozole, DPTU—Diphenyl thiourea, DPG—Diphenylguanidine, DIXP—diisopropylxanthogen polysulfide, DIX—Diisononylxanthogen, XS—Xanthogen sulfide, Wingstay L—butylated reaction productof p-cresol and dicyclopentadiene, Aquanox L—aqueous dispersion ofbutylated reaction product of p-cresol and dicyclopentadiene,AO2246—2,2′-methylene-bis-(4-methyl-6-t-butylphenol),AO264—2,6-di-tert-butyl-4-methylphenol, and MMBI—4- and5-methyl-2-mercapto-benzimidazole.

Henderson (International Latex Conference 2000, Akron, Ohio) disclosed aformulation using sulfur, three accelerators (ZDEC, ZMBT and DPG, eachat a fixed level), zinc oxide, and an antioxidant (Wingstay L).

Wang et al. (U.S. Pat. No. 6,828,387) disclosed formulations usingsulfur, three accelerators (ZDEC, ZMBT and DPG, at different ratios),zinc oxide, and an antioxidant (Wingstay L).

Sak et al. (U.S. Pat. No. 6,618,861) disclosed a formulation usingsulfur and a sulfur donor (TMTD), four accelerators (ZMBT, ZDEC, ZDBCand DPTU, each at a fixed level), zinc oxide, and two phenolic typeantioxidants (A02246 and A0264).

Chakraborty et al. (2nd International Rubber Glove Conference 2004,Kuala Lumpur, Malaysia) disclosed formulations using sulfur, twocombinations of two accelerators (ZDNC and DIXP, or ZDEC and MBT), zincoxide, and two antioxidants (A02246 and MMBI).

Webster et al. (International Latex Conference 2004, Akron, Ohio)disclosed formulations using sulfur, undisclosed accelerator systems,zinc oxide, and an undisclosed antioxidant.

Jole Van (WO 2007/017375) disclosed formulations using sulfur, twoaccelerators (ZDEC and DPG), zinc oxide, and an antioxidant (Aquanox L).Jole Van (WO 2007/017368) also disclosed formulations using sulfur,accelerators (DIXP, and alkyl dithiocarbamates of various chain lengths,such as ZDNC, and DPG), zinc oxide, and an antioxidant (Aquanox L).

Lucas (WO 2003/072340) disclosed formulations using sulfur, accelerators(various combinations comprising DIXP, DIX, XS, TETD, TBeTD, and ZDBeC),zinc oxide, and an antioxidant (Wingstay L).

Teoh et al. (U.S. Pat. No. 7,179,415) disclosed a neoprene articleformed using sulfur, zinc oxide, and accelerators (Rhenocure, DPG, andZDBC), from 1.0 to 3.0 phr of an antioxidant (e.g., Wingstay L), andfrom 0.5 to 2.0 phr of an anti-tack agent (e.g., Michem Lube-180).

Bourne et al. (U.S. Pat. No. 6,195,805) disclosed a neoprene articleformed using a vulcanizer, an activator, an accelerator, from 0.25 to5.0 phr of an antiozonant, and from 0.1 to 3.0 phr of an antioxidant.The neoprene articles were packaged in paper and then sterilized usinggamma irradiation or electron beam sterilization.

Weikel et al. (U.S. Pat. No. 6,306,514) disclosed elastomeric flexiblearticles having a lubricant composition provided on the skin-contactinglayer, in order to improve lubricity. The elastomeric base layer may beformed from a synthetic rubber latex emulsion that includes a sulfur orsulfur-containing vulcanizer, a zinc oxide activator, a dithiocarbamateaccelerator, a phenol-type antioxidant, and an emulsified wax as anantiozonant.

Accordingly, there is a need in the art for methods of packaging andsterilizing elastomeric articles in a manner that prevents and/orminimizes degradation to the articles, particularly degradation that maybe caused and/or accelerated by sterilization techniques such as gammairradiation, x-ray irradiation, and electron-beam processing. There isalso a need for packaged elastomeric articles produced according to themethods of the invention. Such packaged elastomeric articles exhibitimproved degradation-resistance as compared to elastomeric articles thatare not packaged in accordance with the methods of the presentinvention. The packaged elastomeric articles beneficially exhibit areduced incidence of cracking and discoloration, regardless of whetherthey are subjected to sterilization techniques.

SUMMARY OF THE INVENTION

It has been discovered that elastomeric articles, especially thoseformed from polymers other than natural rubber, such as those havingunsaturations in the polymer chain, and particularly synthetic PI, canshow signs of degradation by ozone and other degradants (e.g., oxygenand reactive oxygen species) even when they remain in an unopenedpackage. The degradation can be particularly problematic when theelastomeric articles have been subjected to radiation-basedsterilization techniques.

The present invention meets the unmet needs of the art, as well asothers, by providing methods for packaging elastomeric articles so thatthey are more degradation-resistant, and exhibit reduced cracking and/ordiscoloration (which may take the form of a whitish surfacediscoloration), particularly after being subjected to sterilization orother processes that accelerate degradation of elastomers. The presentinvention is further directed towards methods of reducing degradation ofelastomeric articles that may be subjected to sterilization techniques.Such elastomeric articles may contain antidegradants, such asantioxidants and/or antiozonants, and may be provided in a package thatmaintains a reduced-oxygen environment therein, in order to provideresistance to degradation. The elastomeric articles and methods of theinvention are particularly beneficial for avoiding problems associatedwith degradation in synthetic PI latex articles.

According to one aspect of the invention, the invention relates to amethod of packaging an elastomeric article which prevents and/or reducesdegradation of the elastomeric article. The method includes providingone or more antidegradants, such as antiozonants and/or antioxidants, inthe elastomeric article, placing the elastomeric article in a package,preferably comprising a low-oxygen-permeable material, removing oxygenfrom within the package to form a reduced-oxygen environment inside thepackage, preferably by exposing the package to a vacuum of 250 mbar orless, and sealing the package to provide the elastomeric article withinthe reduced-oxygen environment inside the package. The elastomericarticle provided within the package may be subject to a sterilizationprocedure, preferably by a process comprising radiation.

An additional aspect of the invention relates to packaged,degradation-resistant elastomeric articles that include an elastomericarticle formed from an elastomer comprising an unsaturated polymer andalso comprising an antidegradant such as an antiozonant and/orantioxidant, and a package comprising a low-oxygen-permeable material.The elastomeric article is provided inside the package, and theenvironment inside the package has a reduced oxygen level as compared tothe environment outside the package. According to further aspects, theelastomer may be polyisoprene. In certain aspects, the packagedelastomeric articles exhibit synergistically improveddegradation-resistance as compared to elastomeric articles that do notcomprise the antidegradant and/or are not packaged in accordance withthe methods of the present invention. In certain aspects, theelastomeric articles may be sterile.

Another additional aspect of the invention relates to a method ofpackaging an elastomeric article, including providing one or moreantidegradants, such as antiozonants and/or antioxidants, in theelastomeric article; placing the elastomeric article in a package, wherethe package preferably has a volume that is reduced compared to astandard package; removing oxygen from within the package to form areduced-oxygen environment inside the package, preferably by exposingthe package to a vacuum of 320 mbar or less; and sealing the package toprovide the elastomeric article within the reduced-oxygen environmentinside the package. The elastomeric article provided within the packagemay be subject to a sterilization procedure, preferably by a processcomprising radiation. According to certain aspects, the package having areduced volume may have a volume of about 335 cm³ or less, 280 cm³ orless, or 225 cm³ or less. According to still further aspects, the methodof packaging an elastomeric article is contained in a reduced-oxygenenvironment that contains less than 20 cm³ of trapped oxygen, preferablyless than 16 cm³ of trapped oxygen, more preferably less than 14 cm³ oftrapped oxygen.

According to another aspect, the invention relates to a method ofpackaging an elastomeric article, including providing one or moreantidegradants, such as antiozonants and/or antioxidants, in theelastomeric article; placing the elastomeric article in a package;removing oxygen from within the package to form a reduced-oxygenenvironment containing less than 20 cm³ of trapped oxygen inside thepackage; and sealing the package to provide the elastomeric articlewithin the reduced-oxygen environment. According to certain aspects, thereduced-oxygen environment contains less than 16 cm³ of trapped oxygen.According to still further aspects, the reduced oxygen environmentcontains less than 14 cm³ of trapped oxygen. Providing the elastomericarticle in the reduced oxygen environment beneficially results inreduced ozone attack during sterilization, especially radiationsterilization such as gamma irradiation.

According to a further aspect, the invention relates to a packagedelastomeric article including an elastomeric article comprising one ormore antidegradants; a reduced-oxygen environment surrounding saidelastomeric article, comprising less than about 20 cm³ of trappedoxygen; and a package comprising a low-oxygen-permeable material. Thepackage maintains the reduced-oxygen environment surrounding theelastomeric article.

Other novel features and advantages of the present invention will becomeapparent to those skilled in the art upon examination of the followingor upon learning by practice of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The methods of packaging elastomeric articles beneficially permit theelastomeric articles to exhibit synergistically improveddegradation-resistance as compared to elastomeric articles that do notcomprise the antidegradant and/or are not packaged in accordance withthe methods of the present invention. The packaged,degradation-resistant elastomeric articles that are provided by thepresent invention overcome the obstacles discussed above.

The following definitions are provided to clarify the meaning ofspecific terms:

A “dispersion” is an intermediate between a true solution and a mixture,or suspension. It can also be considered an “emulsion,” which consistsof two liquid phases, a “dispersed phase” of microscopic globs, whichare distributed throughout the “dispersing phase.” In oil in waterdispersion (O/W), the dispersing phase is also named the “aqueousphase.” The dispersed phase of the emulsion used to form the elastomericarticles of the present invention is generally referred to as asynthetic colloidal polymer, wherein the polymer may be prepared viaemulsion polymerization (nitrile, polychloroprene), coordination(Ziegler-Natta) polymerization (cis-polyisoprene) or anionicpolymerization (cis-polyisoprene).

“Latex” was originally referred to as a sap from a rubber tree formaking rubber products. Thus, dispersions, emulsions and latex are allconsidered to be kinetically stable, colloidal systems and these termsmay be used interchangeably.

“Sterilization” refers to any process used to kill or eliminatetransmissible agents, including, but not limited to, fungi, bacteria,viruses, spores, etc. Sterilization techniques may include one or morechemical, radiation, and other techniques, with radiation sterilizationbeing particularly preferred in the present invention.

Preferably the sterilization technique is adequate to kill or restrictthe growth of one or more of the following microbes: coagulase-negativeStaphylococci, Enterococci, fungi, Candida albicans, Staphylococcusaureus, Enterobacter species, Enterococcus faecalis, Staphylococcusepidermidis, Streptococcus viridans, Escherichia coli, Klebsiellapneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Acinetobacterbaumannii, Burkholderia cepacia, Varicella, Clostridium difficile,Clostridium sordellii, Hepatitis A, Hepatitis B, Hepatitis C, HIV/AIDS,methicillin-resistant Staphylococcus aureus (MRSA), mumps, norovirus,parvovirus, poliovirus, rubella, SARS, S. pneumoniae (including drugresistant forms), vancomycin-intermediate Staphylococcus aureus (VISA),vancomycin-resistant Staphylococcus aureus (VRSA), andvancomycin-resistant Enterococci (VRE). It is considered to be withinthe ability of one skilled in the art to determine the type ofsterilizing agent and amount necessary to achieve adequate sterilizationof the article.

According to certain aspects the sterilizing agent is radiation, wherethe sterilizing radiation is selected from gamma irradiation, electronbeam sterilization, or X-ray irradiation. According to one aspect, apackaged elastomeric article may be sterilized by gamma irradiation at aradiation dosage of between 10 kGy and 60 kGy, preferably between 20 kGyand 50 kGy, and more preferably between 29.0 kGy and 43.5 kGy.

Elastomer Dispersions

The elastomeric articles of the present invention may be produced usingany conventional manufacturing methods, e.g., coagulant dipping. Thesemethods utilize dispersions containing the elastomer from which thearticle is to be formed. Preferred elastomers include natural rubber,polyurethane, polybutadiene, polychloroprene (neoprene), nitrile rubber,block copolymers of styrene and butadiene, block copolymers of styreneand isoprene, and polyisoprene. According to certain aspects, aparticularly preferred elastomer is polyisoprene.

The dispersions may also contain one or more different compoundingagents, including antidegradants such as antiozonants and/orantioxidants. The elastomeric articles formed from the dispersion havean antidegradant incorporated therein or thereon in an amount sufficientto prevent and/or reduce the article from exhibiting signs ofdegradation, such as cracking and discoloration. In some aspects, thediscoloration is present on the surface of the article, and may bewhitish in color. The concentration of antidegradants, such asantioxidants and/or antiozonants, that will be required to preventand/or reduce degradation, particularly oxidative and ozone degradation,will vary based on the particular antidegradant being used, the type ofpolymer, the amount of oxygen, ozone, and other reactive oxygen speciesto which the polymer is exposed, and the type of sterilizationtechniques to which the article is subjected.

According to some aspects, an antiozonant is added to an elastomerdispersion that is used to make the elastomeric articles of theinvention. Ozone can severely damage some elastomeric articles, such asthose formed from polymers that are highly unsaturated, likepolyisoprene. When included in the aqueous elastomer dispersion of theinvention, certain high molecular weight polymers, such as waxes, EPDMand hydrogenated polydiene can provide such articles with excellentozone resistance. Waxes form a physical barrier at the surface of therubber which protects against ozone attack. There are two types ofwaxes: straight chain paraffin waxes and branched-chain microcrystallinewaxes. The most widely used antiozonant waxes are blends of paraffin andmicrocrystalline waxes for maximum protection over a broad range ofexposure temperatures. Paraffin waxes are straight-chain hydrocarbonmolecules containing about 20 to 50 carbon atoms. Suitable paraffinwaxes have a melting point of from about 50 to 75° C., preferably 52 to68° C. Microcrystalline waxes are also known as amorphous waxes and arehydrocarbons, similar to paraffin waxes, but the carbon chains arebranched and have higher molecular weight of about 40 to 70 carbon atomsper chain. Other examples of antiozonants that may be used in theinvention may include, but are not limited to alkyl/arylp-phenylenediamines such asN-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine 6PPD,organoclay-antiozonant complexes such as smectite-containing clay withalkyl-aryl-p-phenylenediamine, functionalized benzotriazoles such asN,N-disubstituted para-phenylenediamine, triazines such as tris(N-1,4-dimethylpentyl-p-phenylenediamino) 1,3,5-triazine and tris(N-alkyl-p-phenylenediamino) 1,3,5-triazine, and p-phenylenediaminessuch as N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD). In addition,polymers including waxes such as paraffinic wax (MW=300-500),microcrystalline wax (MW=600-700) (with paraffinic wax) and low MW PEwax (MW=100-1100), polymeric antiozonants such as polymericdiphenyldiamine, and ozone inert polymers such as EPDM and brominatedisobutylene/para-methylstyrene copolymer (BIMSM) may be used asantiozonants. It is preferred that waxes are used. Once particularlypreferred wax is Michem Lube 180. Michem Lube 180 is a blend of carnaubawax and paraffin wax. Carnauba wax is a wax of the leaves of the palmCopernicia prunifera, also known as the fan or carnauba palm. The wax iscollected from the leaves of the carnauba palm by collecting them,beating them to loosen the wax, then refining and bleaching the wax.Another preferred wax dispersion is Antilux 600. Any amount ofantiozonant that is sufficient to prevent and/or reduce ozonedegradation of the finished elastomeric article may be included in theelastomer dispersion, for example, from 1.0 to 7.0 phr, more preferablyfrom 2.0 to 6.0 phr, more preferably from 3.0 to 5.0 phr, and mostpreferably about 4.0 phr.

Suitable antioxidants that may be added to the elastomer dispersioninclude, but are not limited to, hindered phenols such as butylatedhydroxytoluene (2,6-di-tert-butyl-4-methylphenol) and thiodiethylenebis-di-t-butyl-4-hydroxyphenyl propionate, hindered polyphenolics suchas butylated reaction products of p-cresol and dicyclopentadiene,hindered phenol/hindered polyphenolics such as trimethyl-tris(di-t-butyl-4-hydroxybenzym)-benzene or octadecyldi-t-butyl-4-hydroxyphenyl propionate, amines such as a blend of 6PPDwith methyl styrene and bis-alpha-dimethylbenzyl diphenyl amine,mixtures such as zinc mercaptotulumimidazole/phenolic, triazinonederivatives such as triazinone-phenol mixtures, polyaromatic amines suchas poly(m-anisidine), phenolic antioxidant hydrazides such as phenolicswith anhydride copolymer, phenolics such as2,2′-methylene-bis-(4-methyl-6-t-butylphenol), cresols such as2,4-dimethyl-6-(1-methylcyclohexyl)-p-cresol, and styrenated phenols.One particularly preferred antioxidant is butylated reaction products ofp-cresol and dicyclopentadiene (e.g., Wingstay L). Any amount ofantioxidant that is sufficient to prevent and/or reduce oxidation of thefinished elastomeric article may be included in the elastomerdispersion, for example, from 0.5 to 5.0 phr, more preferably from 1.0to 4.0 phr, more preferably from 1.5 to 3.0 phr, and most preferablyabout 2.0 phr.

The elastomeric articles of the present invention may be formed usingelastomer dispersions containing any additional components that may beused in conventional elastomer formulations, such as surfactants, pHadjusting agents, and other adjuvants. The amount of these components istypically not more than about 10%, and is preferably about 2-10% byweight of total dispersion phase solids.

Additives may be used in forming the elastomeric articles, and mayinclude at least one of curing ingredients, non-curing ingredients, andadditional polymers, to be discussed below, with the same, similar ordifferent chemical structures from the elastomer. The total amount ofadditive(s) used is about 0.5-49% by weight of total dispersion phasesolids.

The curing ingredients may include any such ingredients found inconventional elastomer dispersion compounding formulations. For example,the curing ingredients may include, but are not limited to,sulfur/sulfur donors, accelerators (primary and secondary), andsulfur-curing (or vulcanization) activators and peroxidecuring/crosslinking agents which are known to those skilled in the art.

When curing using sulfur, the main curing agent preferably compriseselemental sulfur (generally believed to be in the form of S8, but not solimited). This may be used alone or in combination with a sulfur donor.A sulfurless system can also be used, but this requires a sulfur donor.Sulfur donors may include, but are not limited to thiuram polysulfidessuch as tetramethylthiuram disulfide and tetraethylthiuram disulfide,which also function as vulcanization accelerators, and xanthogenpolysulfides such as butylxanthogen disulfide, CPB, diisopropylxanthogen polysulfide DIXP, and diisopropyl xanthogen disulfide.

Accelerators may include, but are not limited to, dithiocarbamates suchas zinc dimethyl dithiocarbamate (ZDMC), zinc diethyldithiocarbamate(ZDEC), zinc dibutyl dithiocarbamate (ZDBC), zinc dibenzyldithiocarbamate (ZBEC) and zinc pentamethylene dithiocarbamate (ZPD),thiazoles such as 2-mercaptobenzothiazole (MBT), sodium2-mercaptobenzothiazole (SMBT) and zinc 2-mercaptobenzothiazole (ZMBT),thiuram sulfides such as tetramethyl thiuram disulfide (TMTD),tetraethyl thiuram disulfide (TETD and tetrapentamethylene thiuramdisulfide (TPTD), guanidines such as diphenylguanidine (DPG) anddi-o-tolyguanidine (DOTG), and thioureas such as thiourea and diphenylthiourea. One or more accelerators may be used to formulate theelastomer dispersion of the invention.

Activators may include, but are not limited to, zinc oxide, magnesiumoxide and lead oxide. Zinc oxide is the most commonly used vulcanizationactivator. A single accelerator or a synergistic combination ofaccelerators may be used.

Any non-curing ingredients that are conventionally used in elastomerdispersion compounding formulations may be used in the presentinvention. For example, the non-curing ingredients may include, but arenot limited to, antioxidants, stabilizers, plasticizers, anti-ozoneagents, pigments, and fillers.

Colloidal stabilizers including alkalis for pH adjustment, surfactantsand alkaline caseinates such as sodium caseinate may also be added tothe aqueous phase.

Suitable plasticizers that may be added to the elastomer dispersion mayinclude, but are not limited to, fatty salts, mineral oils and esterplasticizers.

Suitable pigments that may be added to the aqueous elastomer dispersionmay include a wide range of natural pigments such as titanium dioxideand iron oxides, and synthetic pigments.

Suitable fillers that may be added to the aqueous elastomer dispersionmay include, but are not limited to, inorganic fillers such as clays,calcium carbonate, talc, and silica and organic fillers such ascrosslinked polymethyl methacrylate, finely divided urethane resinparticles and polyethylene microspheres.

Commercially available PI latex such as Kraton IR401 from KratonCorporation (Houston, Tex.), Isolex available from Medline Industries(Mundelein, Ill.), Aqualast 501 available from Lord Corporation (Erie,Pa.) and LIR-700 available from Kuraray (Japan) may be used to prepareelastomeric articles such as gloves, specifically medical gloves, andmore specifically examination and surgical gloves. However, it isconsidered within the ability of those skilled in the art to preparealternative degradation-resistant elastomeric articles other thangloves, including, but not limited to, condoms, probe covers, dentaldams, finger cots, catheters, and the like, using the guidance providedherein.

Packaging of Elastomeric Articles

The finished elastomeric articles formed from the elastomer dispersionmay also be packaged to reduce the amount of oxygen, ozone, and reactiveoxygen species that are present in the package with the elastomericarticle. The present invention encompasses methods of packaging and/orpreserving any articles formed from elastomers.

Regardless of the type of elastomeric article or the specific packagingtechnique, before the outer package is sealed, preferably as much air aspossible is removed from the package to provide a reduced-oxygenenvironment for the elastomeric article provided within the package, ascompared to the environment outside the package. This may be done byusing one or more of the following techniques:

(a) Removing air from an enclosed compartment (or chamber) in which anelastomeric article, which may optionally be wrapped in an inner packet,is placed. The elastomeric article may be sandwiched between a top webfilm and a bottom web film (which may be provided, for example, in theform of a shallow tray) before sealing the film with heat and pressureto form the outer package. Air may be sucked out from the enclosedcompartment (or chamber) by connecting it to a vacuum pump or otherapparatus before sealing the outer package. This method of packaging isreferred to as thermo “form fill seal” packaging.

(b) Mechanically squeezing out air from the unsealed package includingthe elastomeric article, which optionally may be wrapped in an innerpacket. The elastomeric article then may be sandwiched between a top webfilm and a bottom web film to form the unsealed package before sealingthe package with heat and/or pressure. This method of packaging isreferred to as “platen seal” packaging.

(c) Flushing air out of the unsealed package with an inert gas, such asnitrogen, before sealing the package. This may be done using a “formfill seal” packaging machine where inert gas is used instead of applyinga vacuum to remove the air/oxygen.

Any packaging material and/or technique that is capable of maintaining areduced-oxygen environment within the package may be used in accordancewith the present invention.

Standard packaging techniques for elastomeric articles, such as gloves,expose the package to a reduced pressure of about 320 mbar. Elastomericarticles that are packaged under this pressure level show cracking dueto ozone attack during sterilization, especially gamma irradiationsterilization. However, according to the invention, it has been foundthat exposing the package to a vacuum pressure lower than 320 mbar, suchas 250 mbar or less, preferably 220 mbar or less, more preferably 190mbar or less, or a pressure between 180 mbar to 220 mbar, is useful forovercoming the problem of cracking due to ozone attack duringsterilization, especially radiation sterilization such as gammairradiation. Preferably, a reduced-oxygen environment is produced thatcontains about 30% or less, preferably about 20% or less, of the oxygenthat was present (or theoretically would have been present) in thepackage at atmospheric pressure and room temperature, prior to theremoval of the oxygen.

According to other aspects of the invention, it has been found thatpackaging the elastomeric articles in a package having a reduced volumeas compared to a standard package, and exposing the package to a reducedpressure of about 320 mbar or less, or about 250 mbar or less, or about220 mbar or less, or about 180 mbar or less, is also useful forovercoming the problem of cracking due to ozone attack duringsterilization, especially radiation sterilization such as gammairradiation. According to some aspects, and particularly when theelastomeric article is a glove (which may have a volume of, e.g., fromabout 25 cm³ to about 30 cm³), the volume of the package having areduced volume may be about 335 cm³ or less (i.e., about 332 cm³),preferably about 280 cm³ or less (i.e., about 277 cm³), and morepreferably 225 cm³ or less (i.e., about 222 cm³). Preferably, regardlessof the specific combination of package volume and reduced pressurelevel, the packaged elastomeric article is contained in a reduced-oxygenenvironment that contains less than 20 cm³ of trapped oxygen, preferablyless than 16 cm³ of trapped oxygen, more preferably less than 14 cm³ oftrapped oxygen.

According to further aspects of the invention, it has been found thatpackaging the elastomeric articles, preferably gloves, in a package thatcontains less than 20 cm³ of trapped oxygen, preferably less than 16 cm³of trapped oxygen, more preferably less than 14 cm³ of trapped oxygen,results in reduced ozone attack during sterilization, especiallyradiation sterilization such as gamma irradiation. This beneficialreduction in ozone degradation occurs regardless of the specific methodof packaging used to remove oxygen from the package.

Any packaging material and/or technique that is capable of maintaining areduced-oxygen environment within the package may be used in accordancewith the present invention.

Low-oxygen-permeable materials are those that have an oxygentransmission rate of less than about 1000 cm³.mil/100 in².day.atm,preferably less than 900 cm³.mil/100 in².day.atm, more preferably lessthan 500 cm³.mil/100 in².day.atm, and most preferably less than 250cm³.mil/100 in².day.atm, measured at 77° F. and 0% R.H. Suitable suchmaterials that may be useful for packaging elastomeric articles includebut are not limited to polyethylene (or polythene) and nylon-basedmulti-layer films. Nylon is a generic designation for a family ofsynthetic polymers known as polyamides (PA).

Polyethylene (PE) is a thermoplastic polymer of long chains of themonomer ethylene. PE is classified into several categories based on itsdensity and branching, and the types of PE considered most useful forglove packaging include high density polyethylene (HDPE), low densitypolyethylene (LDPE), and linear low density polyethylene (LLDPE). Insome aspects of the invention, HDPE may be defined by a density ofgreater or equal to 0.941 g/cm³, LDPE may be defined by a density rangeof 0.910-0.940 g/cm³, and LLDPE may be defined by a density range of0.915-0.925 g/cm³.

Ethylene vinyl acetate (EVA) is a copolymer of ethylene and vinylacetate (VA). The weight percent of VA usually varies from about 10 toabout 40%, with the remainder being ethylene. It is a hot melt adhesiveand may be blended with LDPE or LLDPE to provide it with adhesiveproperties during heat sealing of the package.

Oxygen transmission rate of various plastic films are given below inTable 1.

TABLE 1 >12% VA LDPE HDPE LLDPE EVA  Nylon Oxygen 250-840 30-250 250-840515-645 2.6 Transmission Rate* *Oxygen transmission rate was measured inunits of cm³ · mil/100 in² · day · atm, at 77° F. and 0% R.H.

According to some aspects, the package may also comprise one or morecompounds that reduce oxygen, ozone, and/or reactive oxygen species fromthe environment inside the package. The compound(s) may be providedseparately within the package, or may be incorporated into the packagematerial itself.

For example, when the elastomeric articles are gloves, the packaging maybe carried out as follows: A pair of powder-free gloves, a right handand a left hand, are manually cuffed down (by inverting the cuffinside-out) about 10 cm so that the inside surface of the cuff isexposed to the outside. The left hand glove is laid flat in the leftside of the inner web film (or paper) with the thumb exposed outward andthe film wrapped around the glove. Similarly, the right hand glove islaid flat in the right hand side of the inner web film with the thumbexposed outward and the paper wrapped around the glove. One wrappedglove is then flipped over the other to produce a rectangularwallet-shaped packet or wallet. This packet is then packed insideanother outer package comprising a bottom web film and a top web filmwhich is heat and pressure sealed on all sides.

In one embodiment of the invention, a tray measuring about 235 mmlength, about 118 mm width, and about 12 mm height is thermally formedon a bottom web film using a forming die having these dimensions. A pairof gloves wrapped in an inner packet is loaded onto the tray and a topwrap film is laid over the tray to form an unsealed package. Theunsealed package is moved to a compartment (or chamber) which is thenclosed. The compartment is connected to a vacuum pump. The vacuum pumpis switched on to suck out oxygen from the compartment. When thepressure of the air in the compartment drops to the required value(e.g., 180 mbar), the sides of the package are thermally sealed. Thepackaged glove is moved out from the compartment while simultaneouslyanother unsealed package is moved into the compartment. The edges of thesealed package are trimmed off to provide a pair of packaged gloves in asealed package. This may be performed as a continuous operation. Oneexample of a machine for carrying out this process is made by TiromatPowerpack.

These and other aspects of the invention are further described in thenon-limiting Examples set forth below.

EXAMPLES Example 1 Preparation of a Polyisoprene Glove

PI Blue polyisoprene latex was compounded according to the formulationgiven in Table 2. The polyisoprene latex was diluted with water, andsodium caseinate solution was then added to the mixture and stirred atambient temperature. While under continuous stirring, zinc oxide andsulfur dispersions were added to the mixture. This was followed byaddition of accelerator dispersions, ZDEC, ZMBT, and DPG, and thenWingstay L, TiO₂ dispersions, and then Match Blue MPLB pigment. The pHwas adjusted to about 11.0 to 11.5 with ammonium hydroxide or potassiumhydroxide solution. Michem Lube 180 dispersion (pH adjusted to 11.0 to11.5) was then added. The composition was then diluted to about 32.5%solids using soft water. The composition was maintained at a temperatureof 25° C. and stored under continuous agitation for 24 hours at atemperature of less than 25° C.

A cleaned glove former was heated in an oven at a temperature of about100° C. for a period of about 65 seconds so that it reached atemperature of about 58° C. It was then removed from the oven and dippedinto a coagulant (prepared according to the formulation given in Table3) maintained at a temperature of 56° C. for a period of 29 seconds, andthen removed. The coagulant-coated former was placed in a drying oven ata temperature of 100° C. for a period of time sufficient to dry thecoagulant.

The coagulant-coated former was removed from the oven and dipped intothe compounded polyisoprene latex maintained at a temperature of 25° C.for a period of 26 seconds. The coated former was removed and placedinto a pre-heated oven at a temperature of 130° C. for a period of 55seconds.

The coated former was then removed from the oven and placed into waterleaching tank at a temperature of 60° C. for a period of 4.5 minutes.The former was removed from the leaching tank and placed into an oven ata temperature of 70° C. for 30 seconds.

The former was removed from the oven and dipped into a tank containingsilicone emulsion at a temperature of 50° C. The former was removed fromthe silicone tank and while still on the former, the glove was beaded atthe cuff using a beader roller.

The former was then placed into a series of ovens for drying and curingthe glove where the glove moved therethrough at zone temperaturesranging from 110 to 135° C. for a total time period of 11.4 minutes.After exiting the curing oven, the glove was subjected to a post-cureleaching. At this step, the glove was rinsed with water at a temperatureof 70° C. for a period of about 1 minute.

The glove was placed in a slurry tank at a temperature of 55° C. for 30seconds. The slurry composition contained 85.2% water, 14.33% starch,0.4% hydroxyethyl cellulose (Cellosize™ QP 52000), 0.4% sodiumhypochlorite, 0.01% surfactant (Darvan#1) and 0.02% Casatab™ T. Theformer was then placed into a post-slurry oven to dry the glove, therebyproducing the final formed glove. The glove-covered former was cooledand the glove was stripped therefrom.

A control PI Blue glove without Michem Lube 180 was made in a similarway as described above, except that Michem Lube 180 was omitted from theformulation shown in Table 2. The preparation of polyisoprene gloves isfurther described in U.S. Pat. No. 6,828,387 to Wang et al., which isincorporated herein by reference.

TABLE 2 Latex Formulation Ingredient Parts (phr) dry weight Polyisoprene100.00 Soft water to dilute latex Sodium caseinate 0.75 ZnO 0.50 Sulfur1.25 ZDEC 0.50 ZMBT 0.50 DPG 1.00 Wingstay L 2.00 TiO2 1.00 Match BlueMPLB 0.35 Michem Lube 180 4.00 Ammonium hydroxide or pH > 11.0 PotassiumHydroxide for adjusting Final total solids content of latex = 32.5%

TABLE 3 Coagulant Formulation Ingredient % Weight Calcium carbonate 3.60Calcium nitrate 14.7 Surfynol TG 0.20 Cellosize 0.06 Soft water 81.44

The gloves were post-processed by chlorination, which removed powderfrom the gloves and modified the glove internal surface to improvedonning and reduced the grip on the external surface. The gloves may bechlorinated one time where the gloves are inverted to expose theinternal surface for direct chlorination after which they are partiallydried and then re-inverted to the original configuration before finaldrying. Alternatively, if a lower external surface grip is required, thegloves may undergo two rounds of chlorination, one round for theexternal surface and one round for the internal surface. PI Blue glovesunderwent two rounds of chlorination as described below.

The formed gloves were loaded into a chlorinator where they were washedby tumbling with water for 3 minutes for two cycles. The gloves werethen chlorinated in an aqueous solution of chlorine at a chlorinestrength of about 300-350 ppm for 8.3 minutes. At the end of thechlorination cycle, any residual chlorine was neutralized by addition ofcaustic soda solution such that the pH of the neutralized solution wasabout 8 or above. The gloves were tumbled for 4 minutes before thesolution was drained off. The gloves were then washed by tumbling withwater for five times for three minutes each time.

The gloves were then placed in a centrifugal water extractor whereexcess water was extracted out. The gloves were then manually invertedthereby exposing the internal donning surface outside. The invertedgloves were then loaded back into the chlorinator where they underwentanother round of chlorination of the internal surface at a chlorinestrength of about 300-350 ppm for 8.3 minutes. At the end of thechlorination cycle, residual chlorine was neutralized with caustic sodasolution and the gloves washed five times with water as per the firstchlorination cycle.

After chlorination, the wet gloves were transferred to a waterextraction machine and excess water was removed by centrifuging. Inorder to improve the donning of the gloves on moist hands (dampdonning), the gloves were coated with a lubricant. The gloves werecoated by loading them into a washer where they were tumbled with anaqueous solution containing cetyl pyridium chloride (1.56%), siliconeSM2140 (0.5%) and ammonium salt of alkyl phosphate (1.0%). The gloveswere dried in a cyclone dryer at about 55° C. for about 35 minutes.

Surface modification of elastomeric articles using lubricants is furtherdescribed in U.S. Pat. No. 7,566,502 B1 to Chen et al., which isincorporated herein by reference.

The dried gloves were additionally coated with a therapeutic,moisturizing composition containing glycerol (92.24%), citric acid(0.39%), d-sorbitol (2.91%), pantothenol (1.94%), glucono-d-lactone(0.97%), and sodium citrate dehydrate (1.55%). The composition washeated to about 90° C. and then sprayed onto the gloves in a tumblerdryer. At the end of the spraying cycle, the gloves were further driedat 60° C. for about 25 minutes. The cooled gloves were then invertedmanually whereby the donning surface of the gloves was now on theinside. This therapeutic coating composition and method for coating ofgloves is further described in U.S. Published Appl. No. 2008/0020023 byWang et al., which is incorporated herein by reference.

The thickness of the finished gloves was measured to be 0.19 mm at thecuff, 0.21 mm at the palm, and 0.22 mm at the fingers.

The gloves are now ready for packaging.

The following calculations are provided as an estimation of the maximumamount of oxygen trapped in the package at atmospheric pressure (1013.25mbar), and at reduced pressures of 320 mbar, 220 mbar and 180 mbar.

The volume of air trapped in the bottom web tray and the top web thatform the package without gloves (assuming tray volume is the same asthat of the forming die; this would be the maximum volume)=1.2×11.8×23.5cm³=332.76 cm³.

Weight of 1 pair of size 7.5 gloves (i.e., two gloves)=2×12.7 g=25.4 g

Volume of 1 pair of size 7.5 gloves (density 0.93 g/cm³)=25.4÷0.93=27.32cm³

Weight of inner wrap=5.9 g

Volume of inner wrap (density=0.94 g/cm³)=5.9÷ 0.94=6.28 cm³

Volume of trapped air in 1 pair of packed gloves at atmosphericpressure=332.76−27.32−6.28=299.16 cm³

Taking the percentage of oxygen in the air as 20.946%, and atmosphericpressure as 1013.25 mbar, the volume of oxygen trapped in 1 pair ofpackaged glove at atmospheric pressure=(299.16×20.946)÷100=62.66 cm³. Ata pressure of 320 mbar, volume of trappedoxygen=(62.66×320)÷1013.25=19.79 cm³. At a pressure of 220 mbar, volumeof trapped oxygen=(62.66×220)÷1013.25=13.60 cm³. At a pressure of 180mbar, volume of trapped oxygen=(62.66×180)÷1013.25=11.13 cm³.

Another way to reduce the volume of trapped oxygen is by reducing thedimension of the forming die. For example, the depth of the forming diecould be reduced to 10 mm (1.0 cm) or 8 mm (0.8 cm), and the volume oftrapped oxygen can be estimated following the above method. The resultsof these calculations are shown below.

TABLE 4 Volume (cm³) of oxygen tapped at various pressures 1013.25 320250 220 Die/Tray dimension mbar mbar mbar mbar 180 mbar 0.8 cm × 11.8 cm× 23.5 cm 39.43 12.45 9.73 8.56 7.00 1.0 cm × 11.8 cm × 23.5 cm 51.0516.12 12.60 11.08 9.07 1.2 cm × 11.8 cm × 23.5 cm 62.66 19.79 15.4613.60 11.13

Example of package top web film: HDPE film such as PHK331 (supplied byAmcor Flexibles, HDPE/Peel 30) is a white multi-layer peelable top web,using a peelable polymer layer. The film provides an easy peel open packwhen used as a top web in horizontal form/fill/seal packaging of sterilemedical devices. This film has a thickness of 3 mil.

Examples of package bottom web film: MD Film (Amcor Flexibles, EVA/LLDPEblend/EVA) is a high performance, olefin based multi-layer film having athickness of 3.5 mil, and is specially suited for thermoformingapplications such as forming the bottom web tray. MD films seal well toa range of heat seal coated materials.

NCS 70 Film (Amcor Flexibles, PE/PA/PE) is a high performance, nylonbased multi-layer film having a thickness of 70 μm, and is speciallysuited for thermoforming applications and seals well to a range of heatseal coated materials.

The packaged gloves are then sterilized by gamma irradiation at a dosageof from 29.0 kGy to 43.5 kGy.

Example 2 Effect of Antiozonant on Degradation Cracking

It is known that for a rubber article, any surface that is subjected tomechanical stress is more prone to degradation or attack by ozone than anon stressed surface. An ozone-degraded surface would show surfacecracking, the extent of which is dependent on the amount of ozone thatattacks the surface. For a packed glove sterilized as described earlier,the surface that is subjected to more mechanical stress is along thefold line of the cuff. More specifically, the two corners of the foldedcuff are the two points subjected to the highest mechanical stress andare therefore most susceptible to ozone attack. This is found to be truefor gloves packed with sufficient air (or oxygen) trapped in the packageand then sterilized with gamma irradiation where the two corners of thefolded cuff would show surface cracking. For a blue color glove such asPI Blue, the cracking at the two corners of the folded cuff could showup as whitish spots if the cracking is severe. The extent of surfacecracking can be more clearly seen under a light microscope at 50 timesmagnification (or other higher or lower magnification) and the degree ofcracking can be subjectively rated.

The procedure for examining surface cracking under a light microscope isas follows. The outer package of a pair of packed gloves is opened bypeeling and the gloves are taken out from the inner wallet. The glove isturned inside-out to expose the inside donning surface and the twocorners of the folded cuff are marked with a ballpoint pen, each cornerwith a square of about 3 to 4 mm to identify the spots so that they canbe easily located under the microscope. The surface to be examined isthen placed under the microscope set at 50 times magnification and thesurface is appropriately illuminated so that the surface is clearlyvisible and any cracking on the surface is clearly distinguished.

Data obtained by examining gloves for surface cracking are shown inTable 5. These data are used to generate the mean values for surfacecracking ratings that are shown in Tables 7 and 8.

TABLE 5 PI Blue-Cracking Ratings Raw Data Set A Set B Ageing conditionUnaged Aged 70° C., 7 days Unaged Aged 70° C., 7 days Glove PI Blue PIBlue PI Blue PI Blue PI Blue PI Blue PI Blue PI Blue type with MichemLube w/o Michem Lube with Michem Lube w/o Michem Lube with Michem Lubew/o Michem Lube with Michem Lube w/o Michem Lube Experiment MU180 MU320NU180 NU320 MA180 MA320 NA180 NA320 MU_320 MU220 NU_320 NU220 MA_320MA220 NA_320 NA220 Packaging condition 180 mbar 320 mbar 180 mbar 320mbar 180 mbar 320 mbar 180 mbar 320 mbar 320 mbar 220 mbar 320 mbar 220mbar 320 mbar 220 mbar 320 mbar 220 mbar piece# point# 1 1 1.0 1.0 1.03.5 1.0 1.5 2.0 4.0 1.0 1.0 3.0 1.0 2.0 1.5 3.0 2.5 2 1.0 1.5 3.0 2.51.0 3.0 2.5 2.5 1.0 1.5 3.0 1.0 2.0 1.0 2.5 2.0 2 1 1.0 1.5 2.0 3.0 1.01.5 1.0 2.5 1.0 1.0 2.5 1.0 2.5 1.0 4.0 4.5 2 1.0 2.0 1.5 3.0 1.0 1.52.0 2.0 1.0 1.0 2.5 1.5 1.5 1.5 3.5 3.5 3 1 1.0 1.5 1.5 1.5 1.0 1.5 3.01.5 1.0 1.0 3.5 2.5 1.5 1.0 2.5 3.5 2 1.0 1.5 1.5 2.5 1.0 4.5 3.0 3.01.0 1.0 4.0 2.5 1.0 1.0 3.5 3.0 4 1 1.0 2.5 1.0 1.5 1.0 4.5 1.0 4.0 1.01.0 3.5 2.5 1.5 1.0 4.0 3.0 2 1.0 1.5 1.0 1.5 1.0 3.5 2.0 3.0 1.0 1.53.5 2.5 3.0 1.0 4.5 3.5 5 1 1.0 1.5 1.5 1.0 1.0 1.5 1.5 1.5 1.0 1.0 2.01.5 1.0 1.5 4.0 3.0 2 1.0 2.0 1.0 3.0 1.0 1.5 2.5 3.0 1.0 1.0 2.5 1.02.0 1.0 3.5 3.5 6 1 1.0 2.5 1.0 3.5 1.0 1.5 1.0 4.0 1.5 1.0 2.5 2.0 1.51.0 3.5 2.5 2 1.0 2.5 1.0 2.0 1.0 1.5 2.0 3.0 1.0 1.0 2.0 2.0 1.0 1.54.0 2.5 7 1 1.0 1.5 1.0 2.0 1.0 3.0 3.5 3.5 1.0 1.0 2.5 3.0 1.5 1.5 4.02.0 2 1.0 1.0 1.0 2.0 1.0 2.0 3.0 3.5 1.0 1.0 2.5 2.0 1.5 1.0 4.0 3.5 81 1.0 1.0 1.0 2.5 1.0 2.5 2.0 2.0 1.0 1.0 2.5 1.5 1.0 1.0 4.0 3.5 2 1.02.0 1.5 3.0 1.0 3.0 1.0 2.0 1.0 1.0 1.0 1.5 1.5 1.0 4.5 3.5 9 1 1.0 2.01.5 3.0 1.0 2.5 1.0 4.0 1.5 1.5 1.5 2.5 1.0 1.5 3.5 2.0 2 1.0 1.5 1.52.5 1.0 2.0 2.5 3.0 1.5 1.0 1.5 1.5 2.0 1.0 2.5 2.0 10 1 1.0 2.5 1.5 3.51.0 3.0 2.0 2.0 1.5 1.0 2.0 1.5 1.5 1.0 2.5 3.0 2 1.0 2.0 1.0 2.5 1.03.0 1.5 2.0 1.0 1.5 2.0 2.0 3.0 1.0 3.5 2.5 11 1 1.0 2.0 1.0 3.5 1.0 2.01.5 2.0 2 1.0 2.0 1.0 1.5 1.0 3.0 1.0 1.5 12 1 1.0 1.0 1.0 1.5 1.0 3.51.5 4.5 2 1.0 5.0 1.0 3.5 1.0 3.0 1.5 4.5 13 1 1.0 1.0 1.0 2.0 1.0 2.52.5 1.5 2 1.0 1.0 1.0 1.5 1.0 3.0 1.5 1.5 14 1 1.0 1.5 1.0 3.0 1.0 3.01.0 3.0 2 1.0 1.0 1.0 2.5 1.0 1.5 1.0 1.0 15 1 1.0 1.0 1.0 1.5 1.0 1.51.5 3.0 2 1.0 2.5 1.0 3.5 1.0 3.5 1.5 3.5 Average 1.00 1.77 1.23 2.451.00 2.50 1.82 2.73 1.10 1.10 2.50 1.83 1.68 1.15 3.55 2.95 Notes forTable 5: 1. All packaged gloves were sterilized with gamma irradiationat 29.0 kGy to 43.5 kGy. 2. Identification of Experiments: M - gloveshad Michem Lube (4 phr) N - gloves had No Michem Lube U - gloves wereUnaged A - gloves were Aged The numerical value corresponds to thereduced pressure (in mbar) used for packaging the gloves. Hence, MU180 =Unaged gloves with Michem Lube packed at 180 mbar, and NA220 = Agedgloves with No Michem Lube packed at 220 mbar. 3. All gloves contained 2phr Wingstay L

From these raw data, statistical analyses using the student t-test at a99% confidence level were carried out to determine whether the meansurface cracking values of two different groups of experiments were(statistically) significantly different. The results of the t-testanalyses are summarized in Table 6. Surface cracking rating for both theunaged gloves and after ageing at 70° C. for 7 days were determined.However, as a predictive test for cracking, it is preferred to age theglove at 70° C. for 7 days.

TABLE 6 Summary of two samples t-test analysis on Cracking rating of PIBlue gloves Aged # to t1 condition Label Results at 99% CI 1 withMichemLube-220 mbar w/o MichemLube-220 mbar Unaged MU220vs SignificantNA220 difference Aged 70° C., 7 MA220 vs Significant days NA220difference 2 with MichemLube-180 mbar w/o MichemLube-180 mbar UnagedMU180 vs Significant NA180 difference Aged 70° C., 7 MA180 vsSignificant days NA180 difference 3 w/o MichemLube-320 mbar w/oMichemLube-180 mbar Unaged NU320 vs Significant NU180 difference Aged70° C., 7 NA320 vs Significant days NA180 difference 4 w/oMichemLube-320 mbar w/o MichemLube-220 mbar Unaged NU_320 vs SignificantNU220 difference Aged 70° C., 7 NA_320 vs Significant days NA220difference 5 with MichemLube-320 mbar with MichemLube-180 mbar UnagedMU320 vs Significant MU180 difference Aged 70° C., 7 MA320 vsSignificant days MA180 difference 6 with MichemLube-320 mbar withMichemLube-220 mbar Unaged MU_320 vs No significant MU220 differenceAged 70° C., 7 MA_320 vs Significant days MA220 difference 7 w/oMichemLube-320 mbar with MichemLube-180 mbar Unaged NU320 vs SignificantMU180 difference Aged 70° C., 7 NA320 vs Significant days MA180difference 8 w/o MichemLube-320 mbar with MichemLube-220 mbar UnagedNU_320 vs Significant MU220 difference Aged 70° C., 7 NA_320 vsSignificant days MA220 difference 9 with MichemLube-220 mbar withMichemLube-180 mbar Unaged MU220 vs No significant MU180 difference Aged70° C., 7 MA220 vs Significant days MA180 difference 10 w/oMichemLube-220 mbar w/o MichemLube-180 mbar Unaged NU220 vs SignificantNU180 difference Aged 70° C., 7 NA220 vs Significant days NA180difference Notes for Table 6: For gloves that have been aged 7 days at70° C., the following are statistically significant: 1. At a fixedreduced pressure, gloves with Michem Lube (ML) showed less cracking thanthose without ML: 1.1. At fixed pressure of 220 mbar, gloves with MLshowed less cracking than those without ML (MA220 vs NA220). 1.2. Atfixed pressure of 180 mbar, gloves with ML showed less cracking thanthose without ML (MA180 vs NA180). 2. Without using ML, gloves packagedunder reduced pressure showed less cracking than those packaged undernormal pressure: 2.1. Without using ML, gloves packaged under reducedpressure of 180 mbar showed less cracking than those packaged undernormal pressure of 320 mbar (NA180 vs NA320). 2.2. Without using ML,gloves packaged under reduced pressure of 220 mbar gives less crackingthan those packaged under normal pressure of 320 mbar (NA220 vs NA320).3a. With ML, gloves packaged under reduced pressure showed less crackingthan those packaged under normal pressure: 3a.1. With ML, glovespackaged under reduced pressure of 180 mbar gives less cracking thanthose packaged normal pressure of 320 mbar (MA180 vs MA320). 3a.2. WithML, gloves packaged under reduced pressure of 220 mbar gives lesscracking than those packaged under normal pressure of 320 mbar (MA220 vsMA320). 3b. With ML, gloves packaged under reduced pressure showed lesscracking than those without ML but packaged under normal pressure: 3b.1.With ML, gloves packaged under reduced pressure of 180 mbar showed lesscracking than those without ML but packaged under normal pressure of 320mbar (MA180 vs NA320). 3b.2. With ML, gloves packaged under reducedpressure of 220 mbar showed less cracking than those without ML butpackaged under normal pressure of 320 mbar (MA220 vs NA320). 4. With MLor without ML, gloves packaged under lower pressure of 180 mbar givesless cracking than those packaged under 220 mbar (MA180 vs MA220 & NA180vs NA220).

Table 7 shows that removing more oxygen trapped in the glove package andadding an antiozonant (Michem Lube 180) to a glove containing 2 phrantioxidant (Wingstay L) can reduce degradation cracking.

TABLE 7 Cracking of PI Blue as seen under Light Microscope at 50Xmagnification PI Blue with Control: PI Blue 4 phr Michem without MichemLube 180, Lube 180, Crack rating Crack rating Unaged, 1.1 (1-1.5) 2.5(1-4.0)   Normal vacuum, 320 mbar Unaged, 1.1 (1-1.5) 1.8 (1-2.5)   Highvacuum, 220 mbar Aged 70° C./7 days, 1.7 (1-3.0) 3.6 (2.5-4.5) Normalvacuum, 320 mbar Aged 70° C./7 days, 1.2 (1-1.5) 3.0 (1.5-3.5) Highvacuum, 220 mbar Notes for Table 7 crack ratings: (i) PI Blue refers toa PI glove that is blue in color. (ii) To see the cracking better, theglove was lightly stretched with fingers to expose the cracks. Due tothe elastic properties of rubber, small and shallow cracks tend to closeup and are not visible but when lightly stretched these become visible.(iii) For gloves that have no added color pigment, the area to beexamined may be stained blue with a marker pen, if necessary. This givesa better contrast making a small crack more visible under the lightmicroscope. (iv) Rating of Cracks: 1 - No cracking 2 - Slight cracking3 - Moderate cracking 4 - Fairly severe cracking 5 - Severe crackingresulting in a pinhole which is visible when the opposite side isexamined. These ratings could further be extended to 0.5 unit intervals,e.g., 1.5, 2.5, 3.5, 4.5. (v) For each condition, the internal ordonning surface of 10 pieces of gloves was examined. For each glove, the2 corners of the folded glove were examined and rated for cracking. Thecrack rating value shown is the average of 20 values, which is taken asrepresentative of crack rating of the lot of gloves. (vi) Values givenin brackets are the range of the crack rating. (vii) As a predictivetest for cracking, it is preferred to age the glove at 70° C. for 7 daysbefore examining it under the light microscope.

Example 3 Effect of Vacuum Level on Degradation Cracking

Table 8 shows that using a higher vacuum of 180 mbar for packaging giveseven better results. The gloves used in Example 3 have the sameelastomer composition as the gloves of Example 2.

TABLE 8 Cracking of PI Blue glove as seen under Light Microscope at 50Xmagnification Cracking Ratings Glove with 4 phr Control glove withoutMichem Lube 180 Michem Lube 180 NV, NV, HV, 180 mbar 320 mbar HV, 180mbar 320 mbar Unaged 1.0 1.8 1.2 2.5 (1.0-1.0) (1.0-5.0) (1.0-3.0)(1.0-3.5) Aged, 1.0 2.5 1.8 2.7 7 days/70° C. (1.0-1.0) (1.5-4.5)(1.0-3.5) (1.0-4.5) Aged, 1.1 2.3 1.9 3.2 14 days/70° C. (1.0-1.5)(1.5-5.0) (1.0-2.5) (1.5-4.0)

Example 4 Barrier Integrity of Gloves

The barrier integrity of PI Blue gloves with 4 phr Michem Lube 180packed under normal vacuum of 320 mbar and a high vacuum of 180 mbarwere tested by testing for holes in the gloves according to ASTMD5151-06 Standard Test Method for Detection of Holes in Medical Gloves.

Both unaged gloves and gloves that have undergone accelerated ageing at7 days/70° C. were tested and the results are given in Table 9. Thesegloves are from the same lot as those of Example 3.

TABLE 9 Holes in PI Blue glove with 4 phr Michem Lube 180, packagedunder different vacuum levels Unaged Aged 7 days at 70° C. Vacuum, No.gloves No. gloves % No. gloves No. gloves % mbar tested with holes Holestested with holes Holes 180 402 1 0.2 400 0 0 320 200 3 1.5 200 11 5.5

The result shows that gloves packed under high vacuum of 180 mbar had0.2% holes for unaged gloves and 0% for aged gloves compared with 1.5%holes for unaged gloves and 5.5% for aged gloves packed under normalvacuum of 320 mbar.

It is necessary for aged gloves to have a hole level of less than 1.5%to meet regulatory requirements for surgical gloves.

It will, of course, be appreciated that the above description has beengiven by way of example only and that modifications in detail may bemade within the scope of the present invention.

Throughout this application, various patents and publications have beencited. The disclosures of these patents and publications in theirentireties are hereby incorporated by reference into this application,in order to more fully describe the state of the art to which thisinvention pertains.

The invention is capable of considerable modification, alteration, andequivalents in form and function, as will occur to those ordinarilyskilled in the pertinent arts having the benefit of this disclosure.

While the present invention has been described for what are presentlyconsidered the preferred embodiments, the invention is not so limited.To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the detailed description provided above.

What is claimed:
 1. A method of packaging an elastomeric article,comprising: providing one or more antidegradants in the elastomericarticle; placing the elastomeric article in a package made from alow-oxygen-permeable material; removing oxygen from within the packageto form a reduced-oxygen environment inside the package by exposing thepackage to a vacuum of less than 320 mbar; sealing the package toprovide the elastomeric article within the reduced-oxygen environmentinside the package; and sterilizing the elastomeric article while sealedin the package having the reduced-oxygen environment using asterilization process comprising radiation sterilization.
 2. The methodof claim 1, wherein the reduced-oxygen environment contains less thanabout 20 cm³ of trapped oxygen.
 3. The method of claim 1, wherein thereduced-oxygen environment contains less than about 16 cm³ of trappedoxygen.
 4. The method of claim 1, wherein the reduced-oxygen environmentcontains less than about 14 cm³ of trapped oxygen.
 5. The method ofclaim 1 wherein the one or more antidegradants comprise antiozonantsand/or antioxidants.
 6. The method of claim 1, wherein the package has avolume that is reduced compared to a standard package.
 7. The method ofclaim 6, wherein the package having a reduced volume has a volume ofabout 335 cm³ or less.
 8. The method of claim 6, wherein the packagehaving a reduced volume has a volume of about 280 cm³ or less.
 9. Themethod of claim 6, wherein the package having a reduced volume has avolume of about 225 cm³ or less.
 10. The method of claim 1, wherein theoxygen is removed only by exposing the package to vacuum.
 11. The methodof claim 1, wherein the vacuum is 250 mbar or less.
 12. The method ofclaim 1, wherein the vacuum is 220 mbar or less.
 13. The method of claim1, wherein the vacuum is 180 mbar or less.
 14. The method of claim 1,wherein the sterilization process is selected from the group consistingof gamma irradiation, x-ray irradiation, and electron beam processing.15. The method of claim 1, wherein the one or more antidegradantscomprise an antiozonant.
 16. The method of claim 1, wherein theelastomeric article comprises synthetic polyisoprene.